Problem: $ { {3} \times \left[\begin{array}{r}{-2} \\ {4} \\ {1}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{3}\times{-2} \\ {3}\times{4} \\ {3}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-6} \\ {12} \\ {3}\end{array}\right]}$